The overall objective of this study is to determine the earliest stage of osteoarthritis (OA) that can be detected using novel displacement-encoded MRI (deMRI) alone and in combination with conventional imaging and biomarker assays. OA is a debilitating disease that afflicts nearly 20% of people in the US. In an effort to develop an imaging biomarker that noninvasively tracks structural degeneration in cartilage during OA progression, we utilize deMRI for the measurement of mechanical strain in the interior of cartilage explants and intact joints in vivo. With the development of deMRI, we are now ready to assess the utility and translation of deMRI for diagnosing the early structural and mechanical changes to cartilage that may predispose the joint to deterioration but have not yet fully progressed to OA. We will use three established OA models that represent biological, mechanical trauma, and in vivo combined treatments leading to reproducible degeneration patterns. By comparing deMRI, quantitative MRI (qMRI), and biological (e.g. cytokine) assays, we will track the time course of degeneration and identify key molecules that mechanistically explain deMRI changes. We will further identify the best combination of MRI sequences for early OA detection, and will be positioned to perform clinical trials of therapeutic agents for OA treatment in future studies. We will pursue three related specific aims. In Aim 1, we will monitor in vitro how spatiotemporal patterns of 3D cartilage strain are altered by inflammatory cytokines and selective enzymes. To explain strain changes, the corresponding expression of catabolic factors, matrix content, and tissue structure, will also be monitored. In Aim 2, we will measure spatiotemporal changes in 3D cartilage strains following mechanical injury in vitro. An established compressive injury model will be used to study the progression of cartilage structural deterioration and mechanical strain changes detected by deMRI, which will be related to expression of genes known to be up- and down-regulated in cartilage catabolism. In Aim 3, we will compare imaging and biochemical biomarkers in an animal model of OA pathogenesis in vivo. We will temporally compare deMRI to qMRI, histology and histochemical endpoints, and inflammation and matrix degradation biomarkers from serum and synovial fluid. If successful, this work will provide orthopaedic and musculoskeletal communities with (a) a clinical diagnostic tool to evaluate therapeutic agents to target early OA in animal and human trials, (b) the ability to functionally evaluate tissue healing, and repair with emerging tissue engineering methods, and (c) a platform technology to more broadly study mechanical function of load-bearing tissues (e.g. meniscus, ligament) in vivo.